Synthesis and substituent effect study on 13C NMR chemical shifts of 4-(substitue-phenyl)-6-methyl-3-phenyl-4H-1,2,4-oxadiazin-5(6H)-one

• The experimental 13 C NMR chemical shifts (ppm) in 4-(substituted-phenyl)−6-methyl-3-phenyl-4H-1,2,4-oxadiazin-5(6H)-one derivatives were correlated with Hammett substituent constants and Swain-Lupton parameters. • Single regression analysis (SSP) and Multi-linear regression analysis (DSP) were applied. • Polar and resonance substituent effects satisfactorily operate at C=O-C=N and CH carbon of oxadiazine ring. • Excellent correlation was observed for CH 3 carbon of oxadiazine ring. The twelve novel 4-(substituted-phenyl)-6-methyl-3-phenyl-4H-1,2,4-oxadiazin-5(6H)-one derivatives were synthesized by the reactions of N-Substituted-phenyl-benzamide oximes with 2-bromopropionyl chloride. The synthesized 1,2,4-oxadiazin-5-one derivatives were characterized by their physical constants and IR, 1 H NMR, 13 C NMR and LC/TOF-MS analyses data. The experimental 13 C NMR chemical shifts (ppm) (SSC) of the C=O, C=N, CH and CH 3 carbons of these 1,2,4-oxadiazin-5-one derivatives were correlated with the various Hammett substitution constants and Swain-Lupton parameters, using single (SSP) and multi-linear (DSP) regression analysis. Negative ρ I and ρ R values were found for correlations of C=O, C=N and CH 3 carbons (reverse substituent effect). For the other carbon (CH), positive ρ I (normal substitution effect) and negative ρ R (reverse substitution effect) values were calculated by DSP regression analysis. As a result of DSP regression analysis, the 13 C NMR chemical shift of the C=O, C=N and CH carbons of the oxadiazine ring showed a satisfactory correlation ( r > 0.90), while excellent correlation was observed at the CH 3 carbon ( r = 0.99). The 13 C NMR chemical shift values of the C=O, C=N, CH and CH 3 carbons of the p-Br-substituted 1,2,4-oxadiazin-5-one derivative were estimated using the equations obtained by the DSP regression analysis. These predicted 13 C NMR chemical shifts were compared with experimental 13 C NMR chemical shifts for 4-(4-bromophenyl)-6-methyl-3-phenyl-4H-1,2,4-oxadiazine-5(6H)-one derivatives .